Deformation banding in a Nb polycrystal deformed by successive compression tests

Abstract A large-grained Nb polycrystal was successively uniaxially compressed to different cumulative strains to study the evolution of both the microstructure and the orientation of individual grains. After each deformation step, one grain which shows a banded structure was characterized in detail using electron backscatter diffraction (EBSD) to better understand the formation process of the deformation band (DB). The generation of the DB, which is observed after 11.5% reduction, involves the splitting of a transition band (TB) into two rotation fronts moving in opposite directions. These rotation fronts subseuqently evolve into the boundary of a DB whose alignment is associated with the observed primary and secondary slip systems. Post-analysis consists not only of slip system analysis based on image quality maps but also of lattice rotation analysis based on EBSD data. The latter shows that the orientation evolutions in the matrix and the DB are around the same rotation axis, but with opposite sense of rotation. In addition, grains with similar orientation but different deformation behaviors are compared to investigate the underlying difference in the mechanism of grain splitting. It is found that the formation of a DB occurs where a long-range stress field was created at a lower strain. Since the location of this long-range stress field is orientation dependent, whether or not a grain shows a banded structure strongly depends on its initial orientation. At the end of this paper, a mechanism for the formation of a band structure is suggested.

[1]  G. Winther.  Slip patterns and preferred dislocation boundary planes , 2003 .

[2]  I. Dillamore,et al.  The Mechanisms of Recrystallization in Cubic Metals with Particular Reference to Their Orientation-Dependence , 1974 .

[3]  B. Verlinden,et al.  Visualization of grain subdivision by analysing the misorientations within a grain using electron backscatter diffraction , 2005, Journal of microscopy.

[4]  N. Hansen,et al.  Heterogeneous microstructures and microtextures in cube-oriented al crystals after channel die compression , 1998 .

[5]  D. Kuhlmann-wilsdorf.  Deformation bands, the LEDS theory, and their importance in texture development: Part II. Theoretical conclusions , 1999 .

[6]  R. Honeycombe,et al.  Strain hardening in face-centred cubic metal crystals , 1954 .

[7]  D. Kuhlmann-wilsdorf,et al.  Deformation bands, the LEDS theory, and their importance in texture development: Part I. Previous evidence and new observations , 1999 .

[8]  M. Shih,et al.  Misorientation behavior of an aluminum bicrystal with 15.7° symmetric tilt boundary using simple shear , 2007 .

[9]  R. Becker,et al.  Direct observation of orientation change by channel die compression of polycrystalline aluminum—Use of a split sample , 1996 .

[10]  G. Winther,et al.  Dislocation structures. Part II. Slip system dependence , 2007 .

[11]  J. Driver,et al.  Deformation banding mechanisms during plane strain compression of cube-oriented f.c.c. crystals , 2000 .

[12]  Chun‐Sing Lee,et al.  The formation of cube-oriented material and its surrounding in cold rolled FCC metals , 1993 .

[13]  Chun‐Sing Lee,et al.  Deformation banding and copper-type rolling textures , 1993 .

[14]  F. Inoko,et al.  Deformation band evolution in [110] Al single crystals strained in tension , 2005 .

[15]  R. Quey,et al.  Microtexture tracking in hot-deformed polycrystalline aluminium: Experimental results , 2010 .

[16]  J. Driver,et al.  Orientation splitting of cube-oriented face-centred cubic crystals in plane strain compression , 1991 .

[17]  F. Frank,et al.  On the Theory of Kinking , 1952 .

[18]  F. Inoko,et al.  Deformation bands in a [110] aluminium single crystal strained in tension , 2003, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[19]  V. Kafka,et al.  The inhomogeneity of plastic deformation , 1985 .

[20]  H. Poulsen,et al.  Revealing deformation microstructures , 2007 .

[21]  Z. Zhao,et al.  Theory of orientation gradients in plastically strained crystals , 2002 .

[22]  N. Hansen,et al.  Dense dislocation walls and microbands aligned with slip planes—theoretical considerations , 1997 .

[23]  B. Duggan,et al.  Deformation banding and ferrite-type rolling textures , 2001 .

[24]  F. Inoko,et al.  Deformed Structure and Crystal Orientation at Deformation Bands in 〈011〉 Aluminum Single Crystals , 1996 .

[25]  Frank Reginald Nunes Nabarro,et al.  Theory of crystal dislocations , 1967 .

[26]  G. Winther,et al.  Dislocation structures. Part I. Grain orientation dependence , 2007 .

[27]  Xiaoxu Huang,et al.  Electron Backscatter Diffraction Analysis of Recrystallized Grains Formed in Deformation Band in Aluminum Single Crystal , 2001 .

[28]  N. Hansen,et al.  Macroscopic and microscopic subdivison of a cold–rolled aluminium single crystal of cubic orientation , 1998, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[29]  W. Hosford.  The mechanics of crystals and textured polycrystals , 1993 .